This invention relates to a photoreceptor used in electrophotographic machines such as photocopying machines, laser printers, facsimiles, etc., and particularly to an improved photoreceptor formed by exposing a copper phthalocyanine photoconductive film to iodine vapour.
The early photoconductive materials used as photosensitizers in electrophotography were generally inorganic materials such as selenium, cadmium sulphide, zinc oxide, etc. Since inorganic photoconductive materials were disadvantageous due to their high cost and the difficulties they caused in manufacturing, and their toxicity which pollutes the environment, they were gradually superseded by organic photoreceptors which are easy to manufacture, cheaper nontoxic and flexible.
Generally speaking, there are two types of organic photoreceptors: a single layer type and a separate function laminate. The single layer type organic photoreceptor is formed by bonding to a conductive substrate a photosensitive film having a composition consisting of a charge generating material, a charge transporting material and a binder. The separate function laminate comprises a conductive substrate on which a layer of charge generating material is formed by vapor deposition or applying with a brush, and a layer of charge transporting film applied on the charge generating layer. When an organic photoreceptor is illuminated, the charge generating material produces charge pairs, and by means of an electric field, electrons are transmitted through the conductive substrate. Holes are transmitted to the surface of the photoreceptor through the charge transporting material, neutralizing the negative charge on the surface and forming an electrostatic latent image.
Organic charge generating materials are photosensitive organic pigments such as bisazos, anthraquinones, thioindigoes, phthalocyanines. Copper phthalocyanine (Cu-Pc) is a blue-green pigment which has a strong coloring effect, excellent lightfastness, heat-resistance, chemical-resistance, and is inexpensive and nontoxic. Therefore it has been commonly used in the industry of photoreceptors.
There are eight forms of copper phthalocyanine crystals: such as .alpha.-, .beta.-, .gamma.-, .delta.-, .pi.-, .rho.-, .chi.-, .epsilon.-, among which .alpha.-CuPc, .beta.-CuPc, .epsilon.-CuPc are the most popular pigments, and amoung which all have been massproduced. Particularly, .epsilon.-Cu-Pc has a high degree of absorbing light in the region of 780 nm. This region is the wavelength of laser semiconductor. Since the electrophotographic image forming process in a laser printer or a facsimile utilizes the laser semiconductor as a light source, many attempts have been made to improve a charge generating material made from .epsilon.-CuPc. However, .epsilon.-CuPc has a drawback of being insufficiently photosensitive. Therefore, when .epsilon.-CuPc is used as a photoreceptor, it can not produce a latent image of sufficient potential difference and thereby does not provide a clear development.
Japanese Pat. No. 55-161,249 discloses a process for enhancing the photosensitivity of .epsilon.-CuPc by overlaying a sensitizing dye on the surface of .epsilon.-CuPc. However, this process is disadvantageous because the wavelength of the light absorbed by .epsilon.-CuPc is changed upon addition of the sensitizer, and .epsilon.-CuPc has no sensitivity near the infra-red region (780 nm).